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Allium cepa

Also known as: Onion, Garden onion, Allium cepa

Overview

Allium cepa, commonly known as onion, is a widely cultivated bulbous plant and a popular dietary supplement ingredient. It is rich in bioactive compounds, primarily organosulfur compounds (OSCs) and flavonoids, with quercetin being a notable example. These compounds are responsible for its characteristic odor and diverse biological activities. Allium cepa is used both as a food and in supplement form, with research exploring its potential benefits in areas such as antiobesity, anticancer, antidiabetic, and cardiometabolic health. The research on Allium cepa is moderately to highly mature, with multiple systematic reviews and meta-analyses of clinical trials supporting its efficacy. Evidence quality is generally good, with low risk of bias in many studies, though some variability exists in dosing and formulations across different research.

Benefits

Allium cepa offers several evidence-based health benefits, particularly in metabolic and cardiovascular health. A systematic review and meta-analysis of five randomized controlled trials (RCTs) demonstrated that onion intake, especially onion peel extracts, significantly reduced body weight, BMI, waist circumference, and triglyceride levels in obese subjects. Another meta-analysis of RCTs found that onion supplementation improved cardiometabolic parameters, including LDL cholesterol and adiponectin levels, with effects increasing with longer supplementation duration and higher doses. Furthermore, a meta-analysis of prospective studies indicated that high consumption of allium vegetables, including onions, is associated with a reduced risk of various cancers, though more research is needed on the specific effects of supplements versus whole vegetables. While review evidence suggests potential antidiabetic benefits through antioxidant activity and metabolic modulation, high-quality RCT data in this area are still limited. Benefits are most pronounced in obese and metabolic syndrome populations, with cancer risk reduction observed in general populations. The observed weight and lipid reductions were statistically significant, and cancer risk reductions, while modest, were consistent across studies.

How it works

Allium cepa exerts its health benefits through multiple biological pathways. Its primary mechanisms include potent antioxidant activity, which helps reduce oxidative stress throughout the body. It also modulates lipid metabolism, contributing to improvements in cholesterol and triglyceride levels. Allium cepa possesses anti-inflammatory properties and can inhibit tumor growth pathways, which may contribute to its anticancer effects. Additionally, it is believed to enhance insulin sensitivity, potentially aiding in glycemic control. The active organosulfur compounds interact with enzymes involved in lipid metabolism and oxidative stress, while flavonoids like quercetin modulate inflammatory signaling. These actions collectively impact metabolic, cardiovascular, and immune systems, contributing to its diverse health effects. The bioavailability of these compounds can vary by preparation, with onion peel extracts often concentrating active flavonoids for enhanced effects.

Side effects

Allium cepa is generally considered safe, with a low incidence of adverse effects reported in clinical trials. The most common side effects, occurring in less than 5% of individuals, are mild gastrointestinal discomfort. Uncommon side effects (1-5%) include allergic reactions in individuals sensitive to Allium species. Serious adverse events have not been reported in reviewed randomized controlled trials. Caution is advised regarding potential drug interactions, particularly with anticoagulants, due to the antiplatelet effects of organosulfur compounds found in Allium cepa. Therefore, individuals on anticoagulant therapy should consult a healthcare professional before supplementing. Allium cepa is contraindicated in individuals with a known allergy to Allium species. Data on its safety in pregnant or lactating women are limited, so caution is advised for these populations.

Dosage

The optimal dosage of Allium cepa varies depending on the specific preparation and desired outcome. Meta-analyses have included doses ranging from 70 mg to several grams daily, utilizing forms such as onion powder or standardized peel extracts. Higher doses and longer durations of supplementation have been correlated with greater cardiometabolic benefits. While a maximum safe dose is not well-established, clinical trials have used doses up to several grams daily without serious adverse effects. For consistent dosing and potentially stronger effects, standardized onion peel extracts are often preferred over raw onion. Daily supplementation, ideally taken with meals, may improve tolerance and enhance the absorption of its active compounds. Bioavailability can also be enhanced by certain processing methods, and fat-containing meals may improve the absorption of lipophilic compounds present in Allium cepa. No specific cofactors are identified as being required for its efficacy.

FAQs

Is Allium cepa supplementation safe long-term?

Current evidence suggests Allium cepa is safe for short to medium-term use. However, long-term safety data are still limited, and ongoing research is needed to fully assess prolonged supplementation.

Can onions replace medications for obesity or diabetes?

No, Allium cepa supplementation should not replace prescribed medications for obesity or diabetes. It may complement standard therapies, but always consult a healthcare professional before making changes to your treatment plan.

When are benefits typically seen?

The time frame for observing benefits from Allium cepa supplementation can vary. Improvements in cardiometabolic parameters and weight management are typically observed within weeks to months of consistent use.

Are raw onions as effective as supplements?

While raw onions offer health benefits, supplements, especially standardized onion peel extracts, may provide a more concentrated and consistent dose of bioactive compounds, potentially leading to stronger effects.

Research Sources

https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2021.746944/full – This meta-analysis of prospective studies investigated the association between allium vegetable consumption and cancer risk. It found consistent protective associations across various cancer types, although precise dose-response relationships were sometimes limited by heterogeneity in exposure measurement. The study's strengths included its prospective design and stratified analyses, providing robust evidence for the role of allium vegetables in cancer prevention.
https://onlinelibrary.wiley.com/doi/full/10.1002/fsn3.3426 – This systematic review and meta-analysis of five randomized controlled trials examined the effects of onion supplementation on obese subjects. It demonstrated significant reductions in body weight, BMI, waist circumference, and triglycerides, with onion peel extracts proving particularly effective. The study reported a low risk of bias and statistically significant results with clear effect sizes, supporting onion's role in obesity management.
https://pubmed.ncbi.nlm.nih.gov/38056991/ – This meta-analysis of randomized controlled trials focused on the impact of onion supplementation on cardiometabolic parameters. It revealed improvements in LDL cholesterol and adiponectin levels, with effects increasing with higher doses and longer duration of supplementation. The included RCTs had adequate sample sizes and controls, though some variability in formulations was noted as a limitation, providing strong evidence for cardiometabolic benefits.